The present invention relates to a magnetic pole piece for use in a linear pulse motor.
Linear pulse motors provide high performance as reciprocally movable actuator and hence are widely used for feeding devices in various information peripheral devices such as head feeding devices of the electronic printer and photoelectronic reader. Recently there is a strong need for reduction in dimensions and cost of the linear pulse motor as office automation terminals are being reduced in volume and cost. In addition to these requirements reduction in thickness is required for the pulse motor used for feeding the head of the floppy disc drive.
In view of these requirements, the inventor proposed as a coinventor a flat-type linear pulse motor in U.S. Pat. No. 4,578,622 (filed: Oct. 20, 1983) entitled "LINEAR PULSE MOTOR", corresponding to Japanese Patent Applications Nos. 57-188843, 57-198658 and 58-220238, of which disclosure is hereby incorporated by reference. In this flat-type linear pulse motor, magnetic pole teeth are formed in the pole piece members. Although this flat-type linear pulse motor fairly meets the requirements of reducing volume and thickness thereof, but it is in practice rather hard to form very small pole teeth in the pole piece members.
To overcome this drawback the inventor proposed, as a coinventor, a linear pulse motor in a concurrently-filed U.S. patent application, (inventors: Hiroshi NAKAGAWA and Chuzo YAMANISHI) entitled "LINEAR PULSE MOTOR" and corresponding to Japanese Patent Application No. 59-93531 filed on May 10, 1984. The disclosure of this U.S. patent application is incorporated herein by reference. Referring to FIGS. 1-7, there is illustrated this linear pulse motor which includes a primary magnetic flux generating device 1, having four magnetic poles 1A, 1B, 1C and 1D, and a secondary scale 2 linearly movably supported on the magnetic flux generating device 1. This linear pulse motor is operated in the same operating principle as the linear pulse motor disclosed in U.S. patent application Ser. No. 543,927. As clearly shown in FIG. 4, flat magnetic pole members 4-7 are used for magnetic poles 1A, 1B, 1C and 1D. Magnetic pole members 4-7 include head portions 4A, 5A, 6A and 7A and leg portions 4B, 5B, 6B and 7B integrally formed with the head portions 4A, 5A, 6A and 7A, respectively. The magnetic pole members 4-7 substantially have a L shape. The leg portions 4B-7B are attached through machine screws 20 to corresponding yoke members 9 around each of which is wound a coil 3A or 3B. The magnetic pole members 4-7 are disposed in a plane to substantially form in a X shape, as shown in FIG. 1, with the head portion 4A-7A disposed close to each other. Each pair of pole pieces 4,6 or 5,7 has coil 3A or 3B disposed between legs thereof. Pole teeth 8 of each magnetic pole are formed by bonding to the upper surfaces of the corresponding magnetic pole piece members 4,5 or 6,7 a thin ferromagnetic plate 10 having slits 10A formed through it at a predetermined pitch. The thin plate 10 may be an iron plate having typically a thickness from about 0.1 to 0.5 mm. For such a thin plate each slit 10A have a width about 0.3 mm and each land portion 13, which is formed by the slits 10A and serve as pole teeth, have a width about 0.2 to 1 mm. Each plate 10 is provided with a pair of L-shaped portions 16 and 17 or 18 and 19 (FIG. 5) bonded by adhesive such as epoxy resin to corresponding pole piece members 4 and 5 or 6 and 7. A permanent magnet 11 having specific polarity is bonded to the lower faces of the magnetic pole pieces 4-7 to be magnetically coupled to magnetic poles 1A, 1B, 1C and 1D.
In manufacturing the above-mentioned magnet flux generating device 1, a pole piece blank 12 is previously formed, in which the four magnetic pole members 4-7 are, as shown in FIG. 5, integrally formed so that they are disposed at relative positions at which they are to be assembled later to form the magnetic poles. Further, a thin plate blank 14 having two thin plates 10 integrally formed with it is prepared. Each thin plate 10 has two portions corresponding to the head portions 4A, 5A or 6A, 7A of the pole pieces and provided with slits 10A at predetermined pitch. The thin plate blank 14 is bonded to the pole piece blank 12 to form a bonded assembly, which is then attached to the permanent magnet 11 by bonding the latter to the lower face of the pole piece members 4-7 of the pole piece blank 12. Thereafter, unnecessary connecting portions 12A of the pole piece blank 12 and unnecessary connecting portions 14A of the thin plate blank 14 are cut off by cutting along the broken lines shown in FIGS. 6A and 6B.
This process of manufacture enables easy and accurate relative positioning of the pole piece members 4-7. However, when the connecting portions 12A and 14A are cut off, there is a possibility that excess stress is produced in the pole teeth and the bonding layer, thus resulting in separation of the bonded parts and in deformation of the slit plate 10. Further, the cutting off of the connecting portions 12A and 14A is rather laborious and reduces yield of the magnetic poles.